1. Field of the Invention
The present invention relates generally to speed change gears and more particularly to speed change gears suited for applications with fluid couplings or torque converters used upon vehicles, especially automobiles.
2. Description of the Prior Art
It is desirable that the gear type speed changer of automatic transmissions used upon large automotive vehicles, such as for example, trucks and buses should be capable of shifting between at least four forward speeds and operating with one reverse speed. This speed changing mechanism may be realized by suitably combining three, four or even more simple sets of planetary gears of the single pinion or the double pinion type, of which a variety of combinations may be considered. Within any combination of such planetary gear sets, the following conditions are desired to be satisfied:
(1) The output shaft should be coupled to the same elements within each speed range.
(2) In order to reduce the circumferential speed of the bearing of each element of the planetary gear set, the number of its revolutions should be small.
(3) The tooth load, that is, the tangential force, of each element should be small so as to maintain the strength of the gear teeth.
(4) The gear set should meet the meshing conditions for the number of teeth. The sun gear whose diameter is minimized, as well as each planetary pinion gear, should have the necessary number of teeth.
(5) Within each planetary gear set, the coupling relationship among the elements should be simple and the distance from each other be short.
(6) When attaining speed shifts by frictional coupling means during forward drive, such speed shifts should be available through one coupling means alone.
Conventional apparatus failed to efficiently attain these conditions.